About 20 years ago I recycled and modernized a very old nixie clock built from my father in the 70's, with an 87C51 and a DCF77 module which replaced digital ICs and 50 Hz derived timebase.
This has worked regularly for many years, but in the last years the DCF77 reception has (in my house) become more and more difficult probably from electromagnetic interferences of modern switching PSU, so I decided to cut down the radio reception and implement some form of NTP client...
Did you know that the fantastically cheap and powerful ESP8266 module can be easily programmed in Arduino style ? (With all the benefits of libraries.)
Here you can find everything that is needed and the (few) steps to install the environment in the Arduino IDE.
This is the result... DCF77 radio module emulated with a single and cheap ESP8266 module connected to my home Wi-Fi network
One only output pin is required, the GPIO2 to drive the old nixie clock.
Note to implementation
Apparently the ESP module will hang if you drive low the GPIO2 pin when bootup. So the system works if you connect it to an LED (the thresold level of 2 V is probably enough) but you cannot drive an NPN transistor to interface your clock I solved because my clock need a drive low input, so I use an 1N4148 with the cathode in ESP side, but you must care of it...
The project use the extra Time library which I Included.
The schematic is divided in two: the left is the clock application while the right is a small serial programmer for the esp module if you haven't one.
30/12/2015 software update
changed main loop. Added a mechanism to re-connect wlan after time get failure or wlan loss. After this seems much more stable. Before now we had no more time updates if the AP was restarted.